Integrated circuit (IC) devices often are configurable by a downstream vendor or other customer to store sensitive information, such as an encryption/decryption key, a serial number, and the like. However, debug interfaces in such IC devices often pose a security risk in that they can be manipulated to gain unauthorized access to the secure information. Accordingly, customers often request that IC manufacturers provide some mechanism that allows the customer to disable access to the debug interface. Often, this is accomplished by blowing a fuse associated with the debug interface so as to disable access via the debug interface.
When an IC device is determined to be potentially defective, it often is advantageous to return it to the manufacturer for hardware evaluation (i.e., a “field return”). However, as the customer typically has disabled access to the debug interface, the manufacturer conventionally must resort to complex and expensive techniques to regain access to the debug interface for hardware evaluation. Typically, access to the debug interface is regained by using focused ion beam (FIB) modification to blow a counterpart fuse in the IC device to regain access to the debug interface. FIB modification, however, poses a number of problems. For one, FIB modification requires the use of expensive and complicated equipment and often is unsuccessful regardless. For another, FIB modification often requires destructive deencapsulation of the IC device and thus can prevent future evaluation. FIB modification also results in an override of the customer configuration, thereby preventing subsequent access to such configuration information for further analysis. FIB modification also is relatively temporary due to metal migration, which at some point reconnects the blown counterpart fuse and returns the IC device to a state whereby the debug interface is inaccessible. Accordingly, an improved technique to gain access to the debug interface of a previously-secured IC device for hardware evaluation would be advantageous.